Refactor http timeouts

[asvetlov]

The PR respects --network-timeout option in logs and cp operations.

Code cleanup as a side effect.

[codecov]

Codecov Report

Merging #703 into master will increase coverage by 1.55%.
The diff coverage is 94.11%.

@@            Coverage Diff             @@
##           master     #703      +/-   ##
==========================================
+ Coverage   90.43%   91.99%   +1.55%     
==========================================
  Files          40       40              
  Lines        3230     3234       +4     
  Branches      445      445              
==========================================
+ Hits         2921     2975      +54     
+ Misses        237      196      -41     
+ Partials       72       63       -9

Impacted Files	Coverage Δ
neuromation/cli/job.py	91.09% <0%> (+0.42%)	⬆️
neuromation/cli/rc.py	93.43% <100%> (+0.89%)	⬆️
neuromation/api/storage.py	100% <100%> (+2.28%)	⬆️
neuromation/api/jobs.py	93.24% <100%> (+0.04%)	⬆️
neuromation/api/core.py	98.33% <100%> (+0.18%)	⬆️
neuromation/cli/storage.py	76.59% <100%> (-0.49%)	⬇️
neuromation/cli/main.py	60.91% <0%> (+0.5%)	⬆️
neuromation/cli/formatters/jobs.py	99.52% <0%> (+0.95%)	⬆️
neuromation/cli/utils.py	92.61% <0%> (+1.97%)	⬆️
... and 4 more

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